* {
    margin: 0;
    padding: 0;
}

.box {
    width: 400px;
    height: 200px;
    border: 10px solid #333;
    margin: 30px auto;
    position: relative;
}

img {
    width: 400px;
    height: 200px;
    cursor: pointer;
}

ul {
    position: absolute;
    right: 20px;
    bottom: 20px;
}

ul li {
    width: 30px;
    height: 30px;
    border-radius: 50%;
    display: inline-block;
    background: indianred;
    text-align: center;
    font: 16px/30px '微软雅黑';
}

ul li.active {
    background: red !important;
}

.lf {
    width: 40px;
    height: 40px;
    position: absolute;
    left: 0;
    top: 50%;
    transform: translateY(-50%);
    background: salmon;
}

.rg {
    width: 40px;
    height: 40px;
    position: absolute;
    right: 0;
    top: 50%;
    transform: translateY(-50%);
    background: salmon;
}